1. Field of the Invention
The invention relates to the clarification of deinking process waters which result from the recycling of paper. More specifically, the present invention relates to the use of copolymers containing vinylamine as water clarifying agents in said processes.
2. Description of the Prior Art
Recycled fiber has become an important element in the pulp and paper business. As the desire to recycle grows, the scope of materials recycled is likely to widen. New printing processes, both in the office and the press, are presenting new challenges for recyclers. Established mill recycling programs are working to keep pace with the new technologies, and for the most part have had a surprising amount of success. However, the water-based inks used in flexographic newspaper printing are proving difficult to handle, according to paper producers, who say an excess of the ink causes a reduction in brightness when passed through existing deinking systems.
One of the preliminary manufacturing steps in using recycled fibers for paper making consists of repulping the paper sources followed by removal of the printing ink from the fibers. Large volumes of water are required for the ink removal process and its clean-up is typically accomplished using a solids/liquid separation unit operation, such as Dissolved Air Flotation (DAF). Because recycle mills are most frequently located in metropolitan areas, a high degree of emphasis is placed on maintaining a closed water cycle in the mill. Effective clean-up of the DAF influent becomes important because any residual ink remaining in the water may be reintroduced to the fibers, resulting in a loss of brightness to the final sheet.
Clarification chemicals are typically used in conjunction with DAF units to remove the suspended solids from the deinking process waters. Often deinking process waters have a large anionic charge demand requiring the use of a dual polymer program for effective cleanup. A dual polymer treatment generally comprises a low molecular weight cationic coagulant in combination with a high molecular weight flocculant. Typical cationic coagulants are homo- and copolymers of diallyl dimethyl ammonium chloride, condensation polymers of ethylene dichloride-ammonia or dimethylamine-epichlorohydrin. Acrylamide-based flocculants are used to assist in the solid liquid separation. Both anionic and cationic flocculants can be employed.